1. Field of the Invention
The present invention relates to a waterproof structure of an electric-circuit-containing box for containing an electric circuit including electronic parts, a board and the like.
2. Related Art
A power window switch to open/close a window is provided in an arm rest of a door of an automobile, an inside wall surface of the door, or the like. In general, the power window switch includes an operation button to be operated by hand, a detection switch whose electrical state is switched according to the operation state of the operation button, and the like. The detection switch is mounted on a board on which a circuit is formed. The board, the detection switch and the like are disposed in a box including an upper case and a lower case. The operation button is disposed on the upper case. The box is fixed to the inside of the arm rest or the like so that the operation button protrudes from the arm rest of the door or the like.
Among boxes as described above, some box is assembled such that as disclosed in, for example, JP-A-2001-210190 (patent document 1) and JP-A-9-265851(patent document 2) mentioned below, a projection provided on a side of a lower case is fitted into a hole provided in a side of an upper case. In such a box, when moisture attaches to the surface of the power window switch as a result of opening, for example, the door or window at the time of rain, there is a possibility that the moisture flows down from an upper part of the upper case and enters the box through the hole of the side of the upper case by a capillary phenomenon. In the case where the moisture having entered the box is attached to the detection switch, the board or the like, there occurs a problem that a contact of the detection switch, a pattern of the board, and a resist are damaged (short-circuit, corrosion, burnout, peeling or the like). As a result, the power window switch goes wrong.
Then, in order to solve the problem as stated above, in patent document 2, a rib is provided on the side of the upper case so as to surround the hole, and the moisture flowing down from the upper part of the upper case is guided downward by the rib and is drained.
However, in the foregoing structure of patent document 2, in the case where the amount of moisture flowing down from the upper part of the upper case is large so that it gets over the rib, since the moisture flows to the vicinity of the hole of the upper case, there is a possibility that it enters the box from the hole by the capillary phenomenon.